so let’s say you ask an amaleki to kill himself – did you do a mitzva? licheroah it depends, if the mitzva is for the amaleki to be dead, then lemai naphka minah how he became dead, this is like the halacha that you can make a berachah al asiyas maakeh if you ask a goy to make a maakeh for you because at the end of the day your roof now has a maakeh made for it.
However if you say that the mitzva is that you should kill the amaleki then you can’t make him your shliach for you because he’s not a bar chiyuva